In the state of the art, there are different devices for the detection of benzene gas based on photoionisation detectors (PIDs). However, these devices are not completely selective toward benzene, since they present sensitivity toward other gases and other volatile organic compounds (VOCs). However, the detection limit for benzene is not less than 100 ppb. Moreover, said devices do not present selectivity toward benzene at concentrations of a few ppb when other interfering gases are present, as may occur, for example, in the petrochemical industry.
On the other hand, devices have been disclosed which are based on retention tubes that retain different gases with the exception of benzene. However, once again, the detection limit of benzene gas is 100 ppb and a new retention device must be used for each analysis.
Devices have also been disclosed for the detection of benzene based on optical analysis, which use a large number of chips as chemical sensors. Each of these chips contains 10 capillaries or measurement channels, which are filled with a specific reagent of the substance to be analysed. These reagents change colour in the presence of the substance to be detected and the intensity of the change in colour provides information about the concentration thereof. However, these devices have a high cost due to the reagents used and, furthermore, only detect benzene gas in a reliable manner when the latter is present at concentrations in the order of 200 ppb or greater.
Laboratory-scale assays have also been performed to detect benzene gas at lower concentrations, using 10.6-eV UV lamps for the ionisation, but a device has still not been found which selectively detects benzene at an industrial scale operating at ambient temperature, in the presence or absence of oxygen and in environments wherein other interfering gases are also present.
In terms of yield, the devices available in the market may be applied to detect benzene in the range 0-200 ppm, with a precision of 50 ppb. However, these devices still use retention tubes, with the disadvantages mentioned above.
On the other hand, benzene sensors based on carbon nanotubes have also been disclosed. However, the proposed sensors exhibit low sensitivity toward benzene when the latter is in the presence of other components, such as interfering gases. Moreover, the sensors based on carbon nanotubes disclosed only detect concentrations in the order of ppm.
It is worth noting that the devices disclosed are either not reversible and, therefore, a new device must be used for each analysis or measurement, or they have a very low response reversibility after being used for the detection of benzene.
Consequently, as yet there is no device for the selective detection of benzene gas within the range of only a few ppb, which is re-usable for different measurements, operates at ambient temperature and in the presence or absence of oxygen.
Benzene sensors based on metal oxides have also been disclosed in the state of the art, in particular, using gold-doped tin oxide. However, the problems associated with metal oxides are a low selectivity (the sensor responds not only to benzene, but also strongly to CO and NO2, amongst others); they must operate at high temperatures, between 350° C. and 400° C., for a reliable, safe detection of benzene; temporary response drifts associated with changes in the structure of the active layer; and degradation of the electrodes due to the high operating temperatures; in addition to a negative effect on the response of said sensors due to the presence of humidity in the environment to be analysed.
Consequently, as yet there is no sensing device in the state of the art for the detection of benzene gas that presents high sensitivity and selectivity in the order of ppb, which may take measurements at ambient temperature, with the energy savings that this entails, and with greater durability, since degradation of the electrodes caused by use at high temperatures is prevented. Moreover, in the state of the art there is no device with high selectivity toward benzene in the presence of other interfering gases, such as, for example, hydrocarbons such as C2H4, nitrogen oxide, carbon monoxide, amongst the most common. There also are no devices in the state of the art for the detection of benzene gas that are re-usable and maintain the sensitivity and the selectivity during several analyses or measurements.